Tuesday, March 10, 2009

I’m Worried About My Dunbar Number

So this post is kind of whiny and perhaps a bit frivolous, but it’s actually a great set-up for a serious couple of posts I hope to do sometime soon about Magpies and social Corvids in general. Unfortunately, it may be a couple of weeks before I can get to that series, because of life/schedule issues, which I’ll explain in my next post. But anyway, this is top of mind right now, so I’m blogging about it today anyway.

I mentioned recently that with the improving weather I’ve been doing a fair amount of road-biking lately, and in fact the last 2 Saturdays I’ve been out training with teammates. I like the guys on my team, but don’t regularly socialize with any of them in the off-season, so it’s been fun to catch up with some familiar faces. But it’s the unfamiliar faces that have me concerned.

Last Saturday I met up with a couple of teammates. The first I knew- having raced with him a few times- but the other I didn’t recognize. So, being the friendly, outgoing guy I am, I pedaled up alongside him and said , ‘Hi! I don’t think we’ve met before, I’m Alex…” To which he responded, “Yeah we’ve met before. Don’t you remember me? I’m Doug. We rode over to East Canyon Resort last summer.” And apparently, we had met before, but for the life of me I have no memory of “Doug” on that ride, or his name, or anything at all about him.

This wouldn’t be anything worth mentioning, except that it happens fairly often. It seems like several times a year I “meet” people whom I’ve already met, and who remember me well enough, but whom I simply can’t recall meeting. I used to console myself by thinking, Well hey, I’m such an interesting, outspoken guy, I’m just more likely to be remembered than most people. But I don’t think that explanation really holds up; I’m a 40-something married white guy with 3 kids living in Utah who likes to ride bikes. Pretty unusual, huh?

Nor do I think the problem is my memory per se; I remember all kinds of details. Not just details like Awesome Wife’s birthday or our anniversary, but copious plant/lichen/insect details (like in this blog), details, dates and itineraries of road trips decades past, and even my SAT and GMAT scores (from 1981 and 1993, respectively.) I also have this weird, rain-man thing with phone numbers…

No, I am beginning to suspect that the only reasonable explanation for my lame social memory is that I have a low Dunbar number, and therefore, an underdeveloped neocortex.

All About The Dunbar Number

Robin Dunbar is British anthropologist who in the early 1990’s figured out an apparent correlation between the size of social groupings in various species of primates and the size of that species’ neocortex, relative to the rest of its brain.

The mammalian brain is divided into distinct parts that do different things. The cerebellum, for instance, sits down low and in back and handles things like movement and sensory processing. Up on top is the cerebral cortex, which deals with things like memory, awareness, perception, attention and consciousness. The cortex consists of 6 layers, the outermost of which is the neocortex. All mammalian brains share this basic structure; bird and reptile brains don’t.

In rodents and other small mammals, the neocortex is smooth. But in primates, including humans, it’s wrinkled and convoluted, allowing more neocortex to be fit within the volume of the skull. Homo sapiens has the biggest neocortex of all primates.

Tangent: Interestingly, the neocortices of dolphins and whales are even more wrinkled than a human neocortex.

What Dunbar proposed was that the ratio of the volume of a primate’s neocortex to the volume of the rest of its brain- the neocortical ratio- was an indicator of how many stable social relationships that species of primate could maintain. The higher the ratio, the larger the group size in which that species would tend to live naturally. He looked neocortical ratios and mean group sizes of 36 different primate species- from Lemurs to Chimpanzees- and found that such a relationship could be expressed in a logarithmic formula* that appears to be largely correct across most of the species. So for example, a Chimpanzee has a neocortical ratio 3.2. which would predict a group size, or Dunbar number, of 65.2. And by and large these numbers seem to be fairly indicative of what’s observed in the wild; Chimpanzees generally live in groups of between 25 and 80 individuals. Much bigger, and the group usually splits off or breaks up.

*Log10(N) = 0.093+3.389Lo10(CR), where “N” is mean group size and “CR” is the neocortical ratio.

Tangent: There were/are exceptions/problems. An Orangutan has a neocortical ratio of 2.99, which would predict a maximum group size of around 50, but Orangutans are almost always solitary. Outside of the primates, the results are mixed for other mammals. The correlation appears to hold for various canines, but breaks down completely for raccoons and bears. And not to deep-end, but I couldn’t find the neocortical ratio for the Bonobo. It’s got to be pretty similar to that of the Common Chimpanzee, but I know the typical group size is much smaller…

The human neocortical ratio is 4.1, which results in a predicted Dunbar number for humans of 148.

Dunbar’s number is so interesting because there’s all kinds of circumstantial evidence that humans “naturally” favor group sizes of around 150. Neolithic subsistence-farming villages, nomadic hunter-gather clans, even basic military groupings, from the ancient Roman maniple (120 men) to a modern military company (75-200 men) all fall somewhere around this number.

To be sure, there’s been a lot of excessive, overwrought drama around the publicity of the Dunbar number, with everybody latching onto it from neo-tribalists/anarchists (who have used it as part of their justification/manifesto for dismantling modern civilization) to the Swedish federal government (which apparently used it in determining the maximum size for offices of its tax authority.)

But hype aside, I’m inclined to believe in Dunbar’s number, in part because way back in 1986, long before anyone had ever hear of Dunbar or his number, I actually conducted the same “experiment”, albeit with an admittedly very unscientific sample size of… one.

The Young Watcher Conducts An "Experiment"

My junior and senior years in college I lived in a house with 6 other guys. Senior year, about a week or so prior to graduation, 3 of us- “Dan”, “Mark”, and I- were sitting around, talking about how many people we really knew. Our university was a large institution with an undergraduate body of ~8,000 students, and we were musing about how odd it seemed that we went to a school with ~7,997 other kids but we were sure that none of us knew anywhere near that many. So we decided to conduct our “experiment”: For the next hour, we racked our brains, and wrote down a list of everyone Mark knew. It had to be someone whom Mark could pick up the phone, call, and say, “Hi, this is Mark [LAST NAME]”, and they would know exactly who he was, without his having to say something like, “Remember me? I’m the guy who stalked you in ChemE 251 last year? Tall, dark hair? You told me never to bother you again?”

We picked Mark because he was, far and away, our most outgoing, popular, and socially adept housemate. He had many friends and was involved in numerous extracurricular activities. He was musically talented (singer, guitar), active in a singing/dance/theatre group, and a popular performer in numerous events on-campus. Mark was also (again by far) the most popular with the opposite sex, and had a succession of very attractive girlfriends.

Tangent: Curious how life turned out for Mark? He is, hands-down, the most financially successful guy I knew in college (and kept track of.) After 2 years as a chemical engineer working for Farberware, he quit his day job to write jokes for Howard Stern. A few years later he moved to Los Angeles, where he started and later sold his own TV production company, for about a gazillion dollars. (If you’re a reality-show fan, there’s a good chance you’ve seen one of his shows.) Last I heard he was still single, still dating beautiful women (including a former Playboy Playmate. No I didn’t include the link here- this isn’t that kind of blog. But if you’re really curious you can google her yourself. Miss March 1999.) He’s the kind of former schoolmate who might make one green with envy, if he weren’t just such a Darn Nice Guy.

Dan and I had known Mark for close to 4 years by then, and together the 3 of us worked diligently on the list. The final number was… 126. (Yes, it was 20+ years ago, and yes I still remember the exact number. I told you, I have a rain-man number thing.) Add in a couple of family members, some cousins and an aunt & uncle or two, and Mark’s Dunbar number was probably right around 150.

I’ve never repeated the experiment for myself. But I really doubt I could come up with a list of 126- much less 150- people with whom I have “stable social relationships.” Oh sure, I could come up with a list of cousins, former college/high school classmates, past/present coworkers, race teammates, etc. But I don’t have “stable social relationships” with all of these people. I couldn’t just call them up and say, “Hey it’s Alex, how are you doing?” (Well I could, but it’d be like, “Alex who? From where? Ohhhh…. that Alex…”)

Somewhere at home I have a CD full of CATscan images of my brain (legacy of a head injury 4 years ago. Mtn biking accident.) But I certainly can’t tell- and maybe not even a radiologist could tell- much about my neocortical ratio from such images. In any event, if really pressed I think my Dunbar number is probably around 50 or 60. In other words, I am basically a good-looking chimpanzee that somehow learned to speak, ride a bike and hold a steady job. This bothers me sometimes when I stew on it for too long. I wonder if someday I’ll be found out- maybe on one of those new TSA Super-X-Ray machines- and they’ll make me go live in a zoo, or some special home for the neocortically-impaired.

I don’t know if it’s significant, but I usually found myself rooting for the apes in the old Planet Of The Apes movies. Well, except for the 2nd one. Then I was rooting for those telepathic mutants with the skullcaps who lived underground and worshipped the atom bomb. Those guys were way cool.

9 comments:

Apocryphal story about David Starr Jordan, a famous Ichthyologist and president of Stanford University: Jordan was famous for not remembering students. One of Jordan's former students returned for a visit and was having a pleasant, lengthy conversation with Jordan when it became clear that Jordan didn't remember him. So the student says: "You don't remember me, do you Dr. Jordan". To which Jordan replied: "Every time I remember a student I forget a fish."

This post is such a relief since it confirms that when "they" figure me out and remove me from general society I will have good company. Not that I'll remember any of them of course, but they won't either so the days will be filled with pleasant, guilt-free conversation.

If Watcher is closer to chimps, I'm afraid I'm closer to the Orangutan.

In my early years I wasn't very social, but "bloomed" in college and enjoy visiting with almost anyone. But the kids put a crimp in the socializing and my circle has contracted. I can't complain, I still have many good friends and acquaintances and enough opportunities to meet new people.

Speak of which, blogs and other internet social forums provide a new way to socialize. I've met people on the internet that I consider friends - many I've met in person, but not all. As a 40-something married with kids who isn't able to get out as much as I used to, the internet has enabled me to socialize even when sitting at home. The internet has augmented my neocortex.

Alex, was Duncan McGuffy (not sure of the spelling of the last name) among your limited circle in college? Your description of "Mark" sounds awfully similar to Duncan's description of one of his college friends. Not that Duncan would remember me or anything.

Perhaps as interesting as the size of the circle are the intersections of various circles. Someone who's good at math should figure out the likelihood, given an average circle size of 150 or so, that any two humans' circles would intersect. Oh wait, six degrees of separation. Besides, I guess then we're crossing over from biology to sociology.

My word verification is "packwars." Contextually interesting, were it an actual word.

SBJ- the name doesn't ring a bell, but given my low Dunbar #, I don't think we should read too much into that... "Mark" and I attended the U. of Pennsylvania, class of '86. Did Duncan?

Tomo- love the fish story. I'm going to figure out a way to use that line...

KKris- I agree that men are vulnerable to social "contraction" following marriage & kids. (More so it seems, than women, oddly.) And yes I've also liked how the net expands my circle by putting me in touch with people with overlapping interests.

WD- I just hope they let us bring our bikes when they put us in the zoo.

Hmm, yes, people you wouldn't meet otherwise. The closest I get to a bike is when I hit my head on the Husband's while walking thru the garage or utility room. And Utah-- even less often! But thanks to mosses and lichens, here we are...

I didn't even know all this (that's why I read WTWWU). Tell me, what's the Dunbar for dolphins?

Sally- I couldn’t find the Dunbar # for dolphins, but I was able to find neocortical ratios, so I calculated it myself. The neocortical ratio varies based on species, from 3.3 for the Humpback Dolphin to- are you ready?- 5.3 for the Common Dolphin. (Source: Neuronal Bases and Psychological Aspects of Consciousness by C. Taddei-Feretti, Carlo Musio.)

That leads to a Dunbar# ranging from 71 to 346! I’d need to do a bit more research, but I think that high end is way out of whack with reality.

The 5.3 ratio (compared to 4.1 for us) is remarkable, but before we declare dolphins smarter than us… a dolphin brain has a different structure than a human brain, or the brains of most larger-brained terrestrial mammals. Specifically, the 6-layer cortical structure doesn’t seem to be as well evolved/developed. (Interesting tidbit: average human neocortical thickness =2.9mm, average for dolphin = 1.5mm.) Dolphin (and whale) brains appear more similarto what is thought to be a more “primitive” structure, in that they seem to be more like the presumed structure of mammal brains back around 50-70 million years ago or so, which- probably not coincidentally- is around when the ancestors of dolphins and whales are thought to have returned to the sea.

Just ran this by my radiologist wife. She said a CT of the brain would not provide enough detail to measure the neocortex since the overall thickness of the cortex is roughly 2 mm (she estimated this off the top of her head-pun intended). An MRI would be easier to read and measure but even then, the neocortex is an almost cellular level thickness. I would have been happy to have her read your CT to confirm your suspicions but anecdotal evidence is good enough.

Consider "face blindness" or as it is officially called, prosopagnosia. I can remember everything I read and the most obscure details however can't remember faces to save my life so I have diagnosd myself with the aforementioned affliction.